1. Field of the Invention
The present invention relates to a method for repairing the electrodes of a display panel.
The display panels to which the method according to the invention applies can consist, for example, of plasma-display panels, electroluminescent panels, liquid-crystal panels, and so on. These panels comprise two arrays of parallel electrodes formed on both faces of the panel, these faces being positioned in such a manner as to ensure that the two arrays of electrodes are at right angles to each other.
These electrodes are of different types and may accordingly be formed of metal, conductive oxide, and so on. They can be fabricated by means of a number of different technologies such as, for example, evaporation, sputtering, screen-process deposition, photoetching, and so on.
Each panel comprises a considerable number of electrodes which commonly runs to several hundreds and sometimes several thousands. Furthermore, these electrodes are often of fairly small width. By way of example, the electrodes provided in plasma-display panels have a width of 50 to 150 .mu.m with a pitch which varies between 0.2 and 0.6 mm.
The problem which gives rise to concern is the fact that it proves very difficult in practice to construct a display panel in which there is not a single cut electrode.
In the case of fabrication of large-size plasma-display panels, at least one panel out of two on an average comprises one or a number of cut electrodes.
When an electrode is cut, a large part of the electrode does not receive any control signal since electrodes are usually supplied only at one end. In consequence, cutting of an electrode makes it impossible to control several elementary points of the panel, with the result that such a panel is not marketable.
It is possible to restrict the use of display panels solely to those in which no cut electrode is present. However, the production of such panels carries the disadvantage of low efficiency.
This situation consequently points to the advisability of an attempt to repair any electrode cuts which may occur.
2. Description of the Prior Art
In the case of plasma-display panels involving formation of gold electrodes, it is a known practice to repair cuts by depositing a layer of gold on the cut electrodes by hand.
This method does not permit the repair of any cuts which may be detected after voltage has been applied to the panel and which may be caused by the various treatments carried out on the electrodes before the two plates which carry the two arrays of electrodes are hermetically closed by means of a seal.
Finally, this method of repair is not readily applicable to plasma-display panels of the type comprising electrodes in thin layers, and especially electrodes in which provision is made for a top layer of aluminum.
It is a known practice in the prior art to repair cut electrodes by brazing a wire at the unsupplied end of each cut electrode and by connecting said wire to the control signal of the electrode.
This repair can be carried out at any stage of manufacture of the panel since it is only necessary to gain access to the ends of the electrodes, which is possible even after sealing of the panel.
This method of repair by brazed wire is subject in particular to the following disadvantages:
in the case of aluminum electrodes, difficulties are encountered when it is endeavored to produce a satisfactory brazed joint with copper wire, for example, particularly as the electrodes are of small thickness;
there is a potential danger of detachment of the repair wires when the panel is subjected to high stresses, whether such stresses are thermal or mechanical. This is the case when the panel is subjected to vibrations;
it may be difficult to conceal the repair wires from view, especially in the case of panels designed to be observed in transparency;
the presence of repair wires produces changes in level which are liable to hinder the connection of the other contacts;
finally, this repair entails the use of terminals for supplying current to the repair wires whereas these terminals normally have other uses.